Nuo Xu

Characteristics and mechanism of conduction/set process in TiN∕ZnO∕Pt resistance switching random-access memories

The characteristics and mechanism of conduction/set process in TiN∕ZnO∕Pt-based resistance random access memory devices with stable and reproducible nanosecond bipolar switching behavior were studied. The dependencies of memory behavior on cell area, operating temperature, and frequency indicate that the conduction mechanism in low-resistance states is due to electrons hopping through filament paths. We also identify that the set process is essentially equivalent to a soft dielectric breakdown associated with a polarization effect caused by the migration of space charges under a low electric field stress. The generation/recovery of oxygen vacancies and nonlattice oxygen ions play a critical role in resistance switching.

Oxide-based RRAM switching mechanism: A new ion-transport-recombination model

This paper presents a unified physical model to elucidate the resistive switching behavior of metal-oxide-based resistive random access memory (RRAM) devices using the ion-transport-recombination model. In this model, the rupture of conductive filaments is caused by recombination of oxygen ions and electron-low-occupied oxygen vacancies. The transport equations of interstitial oxygen ions in the oxide matrix are introduced to quantitatively investigate the reset speed and other properties such as uniformity, endurance, and reset current. The proposed mechanism was verified by experiments.

Bipolar switching behavior in TiN/ZnO/Pt resistive nonvolatile memory with fast switching and long retention

Highly stable bipolar resistive switching behaviors of TiN/ZnO/Pt devices were demonstrated for the first time. The excellent memory characteristics including fast switching speed (<20 ns for set and <60 ns for reset), long retention (in the order of 105 s) and non-electroforming process were demonstrated. The bipolar switching behaviors can be explained by formation and rupture of the filamentary conductive path consisting of oxygen vacancies. The excellent bipolar switching behavior can be attributed to the significant amount of oxygen vacancies in ZnO film and the effect of TiN layer serving as an oxygen reservoir.

A unified physical model of switching behavior in oxide-based RRAM

Excellent bipolar resistive switching (RS) behavior was achieved in TiN/ZnO/Pt resistive random access memory (RRAM) devices. A unified physical model based on electrons hopping transport among oxygen vacancies along the conductive filaments (CFs) is proposed to elucidate the RS behavior in the RRAM devices. In the unified physical model, a new reset mechanism due to the depletion of electrons in oxygen vacancies and the recovery of electron-depleted oxygen vacancies (VO +) with non-lattice oxygen ions (O2-) is proposed and identified.

Resistive Switching in

Al/CeOx/Pt devices with nonstoichiometric CeOx (1.5<x<2) films were fabricated. The unique resistive switching (RS) behaviors for resistive random access memory applications, including stable and sharp bipolar RS processes and a multilevel and self-stop set process without current compliance and without excessive requirement on a high-voltage electroforming process, were demonstrated. A multifilament switching model based on the distribution characteristics of oxygen vacancies in CeOx films is proposed to explain the observed RS behaviors.

\hbox{CeO}_{x}

We fabricated the TiN/ZrO2/Pt sandwiched resistive switching memory devices. Excellent bipolar resistive switching characteristics, including a large number of switching cycles and highly uniform switching parameters, as well as long retention time were achieved. The improved switching behavior of TiN/ZrO2/Pt could be attributed to the oxygen reservoir effect of TiN electrodes on the formation and rupture of the filamentary conducting paths by modifying the concentration distributions of the oxygen ions and vacancies in ZrO2 thin films. The results demonstrate the feasibility of high performance resistive switching memory devices based on transition metal oxides by using TiN as the top electrode.

Films for Nonvolatile Memory Application

Binary metal-oxide-based resistive memory devices generally show broad dispersions of resistive switching parameters with continuous resistive switching, and this leads to severe readout and control hazards. In this paper, we report improvements of the resistive switching characteristics in TiO2-based resistive memory devices induced by the Gd doping of TiO2 films. The effect of Gd doping on the resistive switching of TiO2-based resistive memory devices is discussed.

Highly uniform resistive switching characteristics of TiN/ZrO2/Pt memory devices

In this paper, TiN/ZrO2/Pt sandwiched resistive switching memory devices were fabricated. The effect of set current compliance on the resistive switching behaviors in TiN/ZrO2/Pt memory device was studied. The different dependence of low resistance state on the set current compliance were observed under the different magnitudes of set current compliance: 1) the average read current was linearly dependent on the set current compliance in the magnitude of low set current compliance; 2) then a weaker dependence of the average read current on the set current compliance was observed in the magnitude of higher set current compliance; 3) when the current compliance is high enough, the unipolar resistive switching behaviors instead of the bipolar resistive switching was shown. A physical model based on oxygen vacancy conducting filamentary paths is proposed to explain the effect of set current compliance on the resistive switching behaviors in TiN/ZrO2/Pt memory device.

Gd Doping Improved Resistive Switching Characteristics of TiO2-Based Resistive Memory Devices

2Theta (degree)

The Effect of Current Compliance on the Resistive Switching Behaviors in TiN/ZrO2/Pt Memory Device

In this paper, the characteristics and mechanism of the transition metal oxide (TMO) based resistive switching memory (RRAM) devices were addressed. The results show that doping in oxide matrix materials, electrode material, and operating mode of the set/reset process may significantly affect the resistive switching behaviors of RRAM devices. Optimizing the dopants and matrix materials, electrode materials, device structure, and operating modes and understanding the related mechanisms are required to achieve the excellent device performance of TMO-based RRAM for the memory application. A unified physical model, based on the electron hopping transport between oxygen vacancies along the conductive filament paths, is used to explain and describe the resistive switching behaviors of the TMO based RRAM devices.